CHEMICAL-KINETICS OF METHYL OXIDATION BY MOLECULAR-OXYGEN

Four fuel-lean mixtures of methane and oxygen diluted in argon were studied behind reflected shock waves at temperatures from 1550 to 2200 K. The reaction progress was determined in situ by state-selective laser absorption of OH radicals and CO molecules. The rate coefficients of the CH3 + Oz reactions were determined via detailed computer modeling with the GRT-Mech 1.2 reaction mechanism and theoretical calculations using the RRKM master equation formalism. The derived rate coefficient expressions, in units of cm(3) mel(-1) s,(-1) are 2.87 x 10(13)e(-15340/T) for the reaction CH3 + O-2 --> CH3O + O and 1.85 x 10(12)e(-10224/T) for the reaction CH3 + O-2 --> CH2O + OH. The experimental rate coefficient of the CH3O + O channel was found to be in good agreement with the canonical variational transition state theory. The potential energy barriers relative to CH3 + O-2 were found to be 15.4 kcal/mol for the CH2O + OH channel and 0.9 kcal/mol for the entrance barrier, the latter indicating a tight transition state. The derived reaction model for the high-temperature oxidation of methyl by molecular oxygen is shown to be self-consistent, in harmony with theory, and in agreement with essentially all experimental data available on this reaction system.